Conventionally, a radar apparatus transmits a transmission wave within a transmission range that is an outside of a vehicle, and then acquires target information of a target, such as a preceding vehicle, by receiving a reflection wave reflected by the target. The target information includes a position and a relative speed of the target. A vehicle control apparatus acquires the target information from the radar apparatus and controls the vehicle based on the target information. Thus, the vehicle control apparatus helps a user drive the vehicle safely and comfortably.
In a case where the preceding vehicle is a relatively tall vehicle, such as a truck, there is a possibility that the radar apparatus receives reflection waves reflected by a rear end portion and other portions of a body of the preceding vehicle. The rear end portion of the body of the preceding vehicle is, for example, a rear bumper thereof. The portion other than the rear end portion of the preceding vehicle is, for example, a bottom (base) portion thereof on which a battery and the like are mounted. In other words, the radar apparatus receives a “direct reflection wave” that is reflected by the rear end portion of the preceding vehicle and that reaches the radar apparatus directly from the rear end portion and also receives a “multipath wave” that reaches the radar apparatus after being reflected by the bottom portion of the preceding vehicle first and then by a road surface.
In a case where a host vehicle is some distance away from the preceding vehicle, the radar apparatus receives the direct reflection wave from the rear end portion of the preceding vehicle and the multipath wave from the bottom portion of the preceding vehicle. Then, the radar apparatus derives target information of targets associated with the reflection and multipath waves and then outputs the target information of the targets to the vehicle control apparatus. The vehicle control apparatus controls the host vehicle based on the target information associated with the rear end portion of the preceding vehicle among the received target information, in order to follow the preceding vehicle because a position of the rear end portion of the preceding vehicle is a closest position to the host vehicle.
However, in a case where the preceding vehicle is the relatively tall vehicle and where the rear end portion of the preceding vehicle is higher than a position of the radar apparatus, the rear end portion of the preceding vehicle sometimes comes out of the transmission range of the transmission wave output by the radar apparatus. Therefore, the radar apparatus does not receive the reflection wave from the rear end portion. In other words, the radar apparatus cannot derive the target information of the rear end portion existing in the closest position to the host vehicle. Therefore, the radar apparatus cannot derive an accurate distance between the host vehicle and the preceding vehicle. As a result, there is a case where the vehicle control apparatus does not control the host vehicle appropriately and there is a possibility that the host vehicle comes into contact with the preceding vehicle.